Thesis advisor: J C. Hepburn / Thesis advisor: Yvette D. Kuiper / Metasedimentary rocks of the Merrimack terrane (MT) originated as a thick cover sequence on Ganderia consisting of sandstones, calcareous sandstones, pelitic rocks and turbidites. In order to investigate the age, provenance and stratigraphic order of these rocks and correlations with adjoining terranes, detrital zircon suites from 7 formations across the MT along a NNE-trending transect from east-central Massachusetts to SE New Hampshire were analyzed by U-Pb LA-ICP-MS methods on 90-140 grains per sample. The youngest detrital zircons in the western units, the Worcester, Oakdale and Paxton Formations, are ca. 438 Ma while those in the Kittery, Eliot and Berwick Formations in the northeast are ca. 426 Ma. The Tower Hill Formation previously interpreted to form the easternmost unit of the MT in MA, has a distinctly different zircon distribution with its youngest zircon population in the Cambrian. All samples except for the Tower Hill Formation have detrital zircon age distributions with significant peaks in the mid-to late Ordovician, similar abundances of early Paleozoic and late Neoproterozoic zircons, significant input from ~1.0 to ~1.8 Ga sources and limited Archean grains. The similarities in zircon provenance suggest that all units across the terrane, except for the Tower Hill Formation, belong to a single sequence of rocks, with similar sources and with the units in the NE possibly being somewhat younger than those in east-central Massachusetts. The continuous zircon age distributions observed throughout the Mesoproterozoic and late Paleoproterozoic are consistent with an Amazonian source. All samples, except the Tower Hill Formation, show sedimentary input from both Ganderian and Laurentian sources and suggest that Laurentian input increases as the maximum depositional age decreases. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

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Thesis advisor: Noah P. Snyder / Dam removal is a widely used river restoration technique. Historically, dams produced hydropower, controlled flooding, and provided water storage, but currently many dams in the United States, specifically low head dams in New England, are obsolete. This study aims to assess the ability of a simple morphodynamic sediment transport model, Dam Removal Express Assessment Model (DREAM-1), developed by Cui et al. (2006a). I compare simulations to a dam removal monitoring project that quantified the physical response of the Souhegan River to the removal of the Merrimack Village Dam (MVD), Merrimack, NH. Pearson et al. (2011) reported results of field monitoring from August 2007-May 2010 and found that the Souhegan River responded to dam removal in two phases: initial rapid incision of impoundment sediment induced by immediate base level drop of 3.9 m (~50% of impounded sediment eroded in ~2 months), followed by an event-driven phase in which impoundment sediment eroded primarily during floods. The reach downstream of the dam showed a similar two-phase response, with rapid deposition in the first three weeks after dam removal followed by bed degradation to the pre-removal elevation profile within a year. I have continued the field methods of Pearson et al. (2011) for the past two survey periods, June 2011 and July 2012. Using five years of comprehensive field data, I conduct a hindcast to compare the sediment erosion and deposition patterns predicted by DREAM-1 to the observed downstream response of the Souhegan River. I model the changes in bed elevation for the downstream and upstream channel reaches at intervals that correspond with the dates of four longitudinal profile surveys and seven annual cross-section surveys. Results of the hindcast show that DREAM-1 predicts channel elevation accurately within one meter and with average discrepancy of ±0.35 m when compared to average channel bed elevations of each cross-section. DREAM-1 successfully simulates two phases of upstream channel response, rapid impoundment erosion followed by a longer period of gradual sedimentation change. However, DREAM-1 erodes to base elevation within 11 weeks after dam removal (erosion of the 88% impoundment sand), leaving little sand for transport during the later survey periods. This overestimation of impoundment erosion is likely the product of limitations of the model, specifically the simplification of channel cross-sections with constant width throughout the simulation. The model assumes uniform lateral sediment transport in the impoundment and does not capture the variation in width due to incision and channel widening. This hinders the ability of the model to simulate some details of the sediment budget developed by Pearson et al. (2011) and extended with recent surveys. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.